Which layer of the Earth is responsible for generating Earth's magnetic field?

• A. Crust
• B. Mantle
• C. Outer Core
• D. Inner Core

Answer: (C)

The magnetic field is produced by the motion of a conducting, liquid layer inside Earth. This layer is the outer core, a molten iron-nickel ocean surrounding the solid inner core. Because the fluid is electrically conductive and is moving due to convection, and because Earth rotates, the moving charges generate electric currents that create magnetic fields. The interaction of these flows with rotation organizes into a self-sustaining dynamo, giving rise to Earth's global magnetic field.

The crust and mantle don’t drive a planetary-scale field: the crust is thin and not a strong enough conductor, and the mantle is too viscous and not in the right state to sustain the necessary convective currents. The inner core is solid, so it doesn’t provide the flowing, conductive motion needed to maintain the dynamo.